DE-OS 2,252,536 discloses a process for the preparation of self-crosslinking binders for cathodically depositable electrocoating paints wherein the hydroxyl groups of epoxy resin-amine adducts are reacted with partially blocked polyisocyanates Although tri- and tetraisocyanates are referred to in a listing of the useful polyisocyanates, only the half, or semiblocked diisocyanates are used in the examples. The reference gives no information on the actual partial blocking of such tri- and tetraisocyanates so as to provide, in essence, a monoisocyanate compound.
As described in numerous references, the half-blocked diisocyanates referred to above can be used for introducing reactive groups into polymers which find application as self-crosslinking, heat-curable paint binders, especially in water-thinnable electrocoating paints. Since only one crosslinking group is introduced at any given time when the customary half-blocked diisocyanates are used, adequate crosslinking of the polymers is not fully achievable with these materials.